1. Field of the Invention
The invention relates to a semiconductor device and a process of fabricating the same, and more particularly, to a structure of a semiconductor device such as a field-effect transistor, and the like, having a Schottky electrode, and a process of fabricating the structure.
2. Description of the Related Art
A field-effect transistor (referred to hereinafter as FET) using a compound semiconductor has been well known, and among FETs, attention has since been drawn to a double-hetero (DH) junction type high electron mobility field-effect transistor (referred to hereinafter as HEMT) as a device capable of gaining high output and high efficiency characteristic. Such a HEMT has been described in, for example, a paper under the title of "High Power Pseudomorphic Double-heterojunction Field Effect Transistors With 26V Gate-drain Breakdown Voltages", by K. Matsunaga, N. Iwata, and M. Kuzuhara, Inst. Phys. Conf. Ser. No. 129, Chapter 9, pp. 749-754 (1992).
Further, among HEMTs, there has been well known a HEMT fabricated by combining a substrate composed of gallium arsenide (GaAs) with a channel layer composed of indium gallium arsenide (InGaAs). The HEMT of such a structure is called a pseudomorphic HEMT (referred to hereinafter as PHEMT) because it has a structure incorporating the channel layer composed of indium galliim arsenide (InGaAs) having a crystal lattice warped due to the lattice constant thereof being different from that of gallium arsenide (GaAs) used for the substrate. In the PHEMT, n-type aluminum gallium arsenide (AlGaAs) is used for an electron supply layer for supplying electrons into a potential well in the channel layer, and AlGaAs without any dopant (.PHI.) implanted is used for a Schottky layer to raise a height of the Schottky barrier of a gate electrode.